Schlechtendal & Chamisso ex C. Presl
Ferns in the genus Azolla have a symbiotic relationship with the cyanobacterium Anabaena azollae, which is a nitrogen fixer.
One species is grown as fertilizer by rice growers in Asia. This genus is a member of a small subroup of ferns which produce two different kinds of spores, microspores, which produce gametophytes with only male parts, and megaspores thousands of times larger, which produce gametophytes with only female parts.
Azolla is the world's smallest fern.
Gila River south of Cliff, Grant County 7 November 1992